U.S. patent application number 11/576814 was filed with the patent office on 2008-09-25 for glass ceramic article with diffusion barrier and method for producing a glass ceramic article with a diffusion barrier.
This patent application is currently assigned to SCHOTT AG. Invention is credited to Ottmar Becker, Michael Bug, Gerhard Hahn, Inka Henze, Veit Luther.
Application Number | 20080233355 11/576814 |
Document ID | / |
Family ID | 35616584 |
Filed Date | 2008-09-25 |
United States Patent
Application |
20080233355 |
Kind Code |
A1 |
Henze; Inka ; et
al. |
September 25, 2008 |
Glass Ceramic Article with Diffusion Barrier and Method for
Producing a Glass Ceramic Article with a Diffusion Barrier
Abstract
In order to avoid haloing when burning in a decoration on a
glass ceramic substrate, the invention provides a method for
producing a decorated glass ceramic substrate, in which a glass
substrate is produced or provided, a layer containing silicon oxide
is deposited on the substrate, decorative ink is applied on the
layer containing silicon oxide and the decorative ink is burned in,
wherein the layer containing silicon oxide is flame-pyrolytically
deposited by sweeping over at least one region of the surface of a
substrate with a flame and hydrolyzing a silicon compound added to
the flame.
Inventors: |
Henze; Inka; (Nieder-Olm,
DE) ; Bug; Michael; (Muehltal, DE) ; Hahn;
Gerhard; (Allenfeld, DE) ; Becker; Ottmar;
(Langen, DE) ; Luther; Veit; ( Hattersheim,
DE) |
Correspondence
Address: |
DeMont & Breyer, LLC
100 Commons Way, Ste. 250
Holmdel
NJ
07733
US
|
Assignee: |
SCHOTT AG
55122 Mainz
DE
|
Family ID: |
35616584 |
Appl. No.: |
11/576814 |
Filed: |
November 3, 2005 |
PCT Filed: |
November 3, 2005 |
PCT NO: |
PCT/EP05/11760 |
371 Date: |
January 14, 2008 |
Current U.S.
Class: |
428/168 ;
427/447; 427/452; 428/172; 428/210; 428/542.8; 65/17.2; 65/17.4;
65/60.2 |
Current CPC
Class: |
C03C 2218/15 20130101;
Y10T 428/24926 20150115; Y10T 428/24612 20150115; C03C 2218/113
20130101; Y10T 428/24579 20150115; C23C 16/545 20130101; C03C
2217/72 20130101; C23C 16/453 20130101; C03C 17/3411 20130101; C03C
2217/42 20130101 |
Class at
Publication: |
428/168 ;
427/452; 427/447; 65/60.2; 65/17.2; 65/17.4; 428/210; 428/172;
428/542.8 |
International
Class: |
C03C 17/34 20060101
C03C017/34; C03C 17/245 20060101 C03C017/245; C03C 17/42 20060101
C03C017/42; C23C 16/453 20060101 C23C016/453; F24C 15/10 20060101
F24C015/10; B32B 18/00 20060101 B32B018/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 3, 2004 |
DE |
10 2004 053 707.0 |
Claims
1. A method for producing a decorated glass ceramic substrate, the
method comprising: depositing a layer containing silicon oxide on a
glass substrate; applying decorative ink is applied on the layer
containing silicon oxide; burning in the decorative ink; and
ceramizing the glass substrate; wherein the layer containing
silicon oxide is flame-pyrolytically deposited by sweeping over at
least one region of the surface of a substrate with a flame and
hydrolyzing a silicon compound added to the flame.
2. The method as claimed in claim 1, wherein the decorative ink is
applied before the depositing of the layer containing silicon
oxide.
3. The method as claimed in claim 1, wherein the decoration is
burned in by ceramizing the substrate.
4. The method as claimed in claim 1, wherein the decorative ink is
applied by printing, electrostatic application, electrophotographic
application, applying a transferable image, spraying or
atomization.
5. The method as claimed in claim 1, wherein at least one of the
substances i) hexamethyldisiloxane (HMDSO), ii)
hexamethyldisilazane (HMDSN), and iii) tetraethoxysilane, is used
as the silicon compound.
6. The method as claimed in claim 1, wherein a combustible gas
having at least one of the components hydrogen, methane, propane,
and butane is used to generate the flame.
7. The method as claimed in claim 1, wherein a flame with an
oxidizing part and a reducing part is generated, and the substrate
is swept over only with the oxidizing part in order to deposit the
layer containing silicon oxide.
8. The method as claimed in claim 1, wherein a flat substrate is
flame-pyrolytically coated on both sides with a layer containing
silicon oxide.
9. The method as claimed in claim 1, wherein the substrate is
additionally coated with an infrared-reflecting layer.
10. The method as claimed in claim 9, wherein the substrate is
coated with a tin oxide layer as the infrared-reflecting layer.
11. The method as claimed in claim 1, wherein the layer containing
silicon oxide is deposited with a layer thickness of from 2 to 100
nanometers.
12. The method as claimed in claim 1, wherein a subregion of the
layer containing silicon oxide is coated with a hydrophobic
coating.
13. The method as claimed in claim 12, wherein a subregion of the
layer containing silicon oxide is coated with a sol-gel layer
containing fluoroalkylsilane.
14. The method as claimed in claim 1 further comprising producing
the glass substrate, wherein the production of the glass substrate
comprises the production of a continuous glass strip by
floating.
15. The method as claimed in claim 1 further comprising producing
the glass substrate, wherein the production of the glass substrate
comprises the production of a continuous glass strip by
rolling.
16. The method as claimed in claim 15, wherein the deposition of
the layer containing silicon oxide comprises deposition on the
glass strip after the rolling.
17. The method as claimed in claim 14, wherein the production of a
glass substrate comprises separation of a section from the glass
strip.
18. The method as claimed in claim 17, wherein the deposition of
the layer containing silicon oxide comprises the deposition of a
layer containing silicon oxide on the individualized substrate
produced by separation.
19. A method for producing a glass ceramic article, wherein a
barrier layer containing silicon oxide is deposited on at least one
side of a substrate of the article by sweeping a flame over it and
flame-pyrolytically hydrolyzing a silicon compound added to the
flame.
20. The method as claimed in claim 19, wherein a granular surface
structure of the layer containing silicon oxide having silicon
oxide grains with a diameter of up to 80 nanometers arranged on the
surface of a dense layer is generated by the flame-pyrolytic
deposition.
21. A glass ceramic substrate that is produced in accordance with
the method of claim 1, which substrate is provided with decoration
by burned-in decorative ink, wherein the decoration is applied on a
flame-pyrolytic layer containing silicon oxide on the
substrate.
22. A glass ceramic substrate that is produced in accordance with
the method of claim 1, which substrate is provided with decoration
by burned-in decorative ink, wherein the decoration is surrounded
by regions of the substrate surface having a flame-pyrolytic layer
containing silicon oxide.
23. The glass ceramic substrate as claimed in claim 21, wherein the
layer containing silicon oxide has a layer thickness of from 2 to
100 nanometers.
24. The glass ceramic substrate as claimed in claim 21, which
comprises a hydrophobic coating on at least one subregion of the
layer containing silicon oxide.
25. The glass ceramic substrate as claimed in claim 24, wherein the
hydrophobic coating comprises a silicate layer containing
fluoroalkylsilane.
26. The glass ceramic substrate as claimed in claim 21, which
comprises a tin oxide layer.
27. The glass ceramic substrate as claimed in claim 21, wherein the
layer containing silicon oxide comprises a granular or corrugated
surface having silicon oxide grains with a diameter of up to 80
nanometers arranged on the layer.
28. A product comprising a glass ceramic substrate that is produced
in accordance with the method of claim 1, the product being one of:
i) a hob plate; ii) an oven window; iii) a baking, cooking, or
frying vessel; iv) crockery; v) a plate of a refrigerator; vi) a
glass ceramic reflector; and vii) a glass ceramic window.
29. An intermediate product for producing a glass ceramic article,
comprising a green glass substrate and a layer containing silicon
oxide flame-pyrolytically deposited thereon.
Description
[0001] The invention relates in general to the production of glass
ceramic articles, and in particular the invention relates to
barrier layers on such articles.
[0002] Many glass ceramic articles, for example glass ceramic hobs,
comprise decorations. In the case of a hob, inter alia there may be
circular decorations which show the edges of the individual hob
plates. Manufacturer information is also often applied.
[0003] For cost reasons, decorative inks are mostly burned in
simultaneously with heat treatment processes, for example
prestressing and/or ceramizing processes on the glass substrates.
With a range of decorative inks, however, visually perturbing
surface effects may in particular occur during the process of
ceramizing the glass substrate to form the glass ceramic. Known in
this regard, in particular are blue to rainbow-colored halos or
edges in the vicinity of the decoration as well as contact tracks
visible due to interference effects during handling or storage.
Inter alia, sucker or paper impressions may remain visible.
[0004] DE3936654C1 describes a method, which describes halo-free
decorative burn-in during the process of ceramizing LAS glass
ceramics. In the method, a silicon oxide layer is applied onto the
starting substrate glass before the decoration, preferably with the
aid of a spray method. However, a disadvantage which has been
revealed in this case is that the SiO.sub.2 layer must be applied
with a relatively large thickness, approximately 100 nm, in order
to effectively prevent halos. The large thickness is required in
order to prevent decorative components such as boron from diffusing
into the green glass. Another disadvantage is the susceptibility of
sol-gel layers to cracking under high temperature conditions and
with large layer thicknesses, which are incurred by subsequent
crosslinking and the resulting shrinkage of the layer.
[0005] Owing to the thickness of the SiO.sub.2 layer, undesired
deformations of the substrate furthermore occur during the
ceramizing process. The effect of the comparatively rigid SiO.sub.2
layer on the upper side is that the substrate becomes deformed in a
dome shape owing to the viscosity reduction associated with
ceramizing and the likewise associated shrinkage process of the
substrate.
[0006] It is therefore an object of the invention to provide
improved glass ceramic substrates having decoration. In an
extremely surprising way, this object is achieved directly by a
method and a glass ceramic substrate according to the independent
claims. Advantageous refinements and configurations of the
invention are specified in the dependent claims.
[0007] Accordingly, the invention provides a method for producing a
decorated glass ceramic substrate, in which a glass substrate is
produced or provided, a layer containing silicon oxide is deposited
on the substrate, decorative ink is applied on the layer containing
silicon oxide, a decoration is produced by burning in the
decorative ink and the glass substrate is ceramized, wherein the
layer containing silicon oxide is flame-pyrolytically deposited by
sweeping over at least one region of the surface of a substrate
with a flame and hydrolyzing a silicon compound added to the flame.
A glass ceramic substrate producible according to the invention is
therefore provided with a decoration of burned-in decorative ink,
the decoration being applied on a flame-pyrolytic layer containing
silicon oxide on the substrate.
[0008] It is likewise possible to apply the decoration before
depositing the layer containing silicon oxide, and then to deposit
the layer containing silicon oxide on the substrate, so that the
decorative ink and the undecorated regions of the surface are
covered by the layer containing silicon oxide. In a method for
producing a decorated or glass ceramic substrate according to this
embodiment of the invention, a glass substrate is therefore
produced, decorative ink is applied on the substrate, a layer
containing silicon oxide is deposited on the surface provided with
the decoration, the decorative ink is burned in and the glass
substrate is ceramized, the layer containing silicon oxide being
flame-pyrolytically deposited by sweeping over at least one region
of the surface of a substrate with a flame and hydrolyzing a
silicon compound added to the flame.
[0009] In both cases--depositing the layer containing silicon oxide
before or after applying the decorative ink, a glass ceramic
substrate produced according to the invention is therefore provided
with a decoration of burned-in decorative ink, the decoration being
surrounded by regions of the substrate surface covered by a
flame-pyrolytic layer containing silicon oxide. In this way,
haloing is effectively avoided.
[0010] By the invention as described here, inter alia, it is
possible to avoid deformation of the substrate as occurs with the
method described in DE 3936654 C1, since it has surprisingly been
found that SiO.sub.2 layers, which are produced by the
flame-pyrolytic method according to the invention, can be much
thinner.
[0011] It has thus surprisingly been shown that depositing a layer
containing silicon oxide with a layer thickness of from 1 to 100
nanometers, particularly preferably 4 to 40 nanometers, and
particularly preferably at most 20 nanometers, is already
sufficient as a diffusion barrier in order to suppress diffusion of
components from or into the substrate. Therefore, haloing on the
decoration is already effectively prevented by such thin layers.
With this small thickness, the aforementioned deformation of the
substrate during the ceramizing process is no longer observed. This
surprising effect is also attributable to the very dense structure
and the resulting improved barrier effect of such flame-pyrolytic
layers containing silicate. Owing to the small thickness, the layer
is also visually inconspicuous, or invisible, so that refractive
index matching by TiO.sub.2 doping as described in DE 3936654 C1 is
not necessary.
[0012] The layer containing silicon oxide may be deposited both
before and after the ceramizing. If the layer containing silicon
oxide is deposited after ceramizing has already taken place, then
the decoration is burned in separately on the glass ceramic
substrate.
[0013] A preferred embodiment of the method relates to the
production of glass ceramic objects, wherein the decoration is
advantageously burned in simultaneously by ceramization of the
substrate. In this case, the layer containing silicon oxide is
accordingly applied before the ceramization. The intermediate
product obtained in this way for the production of a glass ceramic
article, i.e. a green glass substrate with a flame-pyrolytic
coating containing silicon oxide deposited thereon, furthermore
exhibits the surprising property that the flame-pyrolytic layer
containing silicon oxide acts as a covering layer which can avoid
or mitigate the creation of scratches and other superficial damage
during the further processing.
[0014] Besides the barrier effect, the layer may accordingly also
have additional functions. By coating with layers containing
silicon oxide--as in the above example of the flame-pyrolytically
coated green glass or starting glass substrate--protective effects
can be achieved for example against scratching of the glass and
glass ceramic substrates. Possible problems which may occur in the
ceramizing process, for example shrinkage scratches during the
ceramizing and/or adhesion on a transport support, can furthermore
be prevented or reduced. Suitable substrates are inter alia panes
of float glass or rolled glass or glass ceramic produced from these
materials. In order to produce glass ceramic products decorated
according to the invention, such substrates may also be used as
starting substrates or green glass. Such flat substrates, as are
obtained inter alia by floating or rolling, may according to a
refinement of the invention also be flame-pyrolytically coated on
both sides. The flame-pyrolytic coating on both sides may then be
carried out as a base layer for decoration on both sides by
applying the decorative ink on both sides and burning it in.
[0015] If a float glass or rolled glass or a glass ceramic produced
therefrom is used as the substrate, then the production of the
glass substrate comprises the production of a preferably continuous
glass strip by floating and/or rolling. According to one embodiment
of the invention, the layer containing silicon oxide may be
deposited on the continuous glass strip directly after the rolling
of floating. The production of the substrate may furthermore
comprise separation of a section from the continuously produced
glass strip. In this case, it is possible not to apply the layer
containing silicon oxide until on the already individualized
substrate produced by separating a section from the glass strip.
This refinement of the invention is advantageous inter alia because
other processing steps, which may further damage the
flame-pyrolytic coating, follow after the separation of the
substrate. These may inter alia be hot forming steps to produce
curved substrates. Coating after the individualization also makes
it possible to coat a plurality of production lines. This is
advantageous, for example, when products without burned-in
decoration are also intended to be produced on the glass strip.
[0016] The decorative ink may be applied by any method which allows
structured application for generating the decorative pattern. One
possibility, for example, is printing. Screen printing, by which
paste-like inks can also readily be applied, is suitable in
particular. Electrostatic and/or electrophotographic application,
applying a transferable image, spraying or atomization may also be
used for applying the decorative ink.
[0017] At least one of the substances hexamethyldisiloxane (HMDSO),
hexamethyldisilazane (HMDSN), tetraethoxysilane, may be added as
the silicon compound to the flame for depositing the layer
containing silicon oxide. A gas with at least one of the components
hydrogen, methane, propane, butane may furthermore preferably be
used as the combustible gas.
[0018] For the quality of the flame-pyrolytic coating, it has also
been found favorable in particular to generate a flame with an
oxidizing part and a reducing part, and to sweep over the substrate
only with the oxidizing part in order to deposit the layer
containing silicon oxide. In this way, inter alia, deposition of
only partially hydrolyzed silicon compounds or contamination with
combustible gas constituents are substantially avoided.
[0019] The flame-pyrolytic coating according to the invention also
has further advantages. The layer is not only capable of being an
effective diffusion barrier against haloing in the vicinity of the
decoration, against contact artifacts, but also of avoiding
undesired bulging of the substrates during the heat treatment
processes. The layer essentially containing silicon dioxide
furthermore comprises hydroxyl groups--owing to the hydrolysis
process--which in particular are also present on the surface of the
layer. These OH groups cause particularly good bonding and
therefore substantially improved adhesion of layers applied
thereon. This applies in particular for the adhesion of the
decoration. Moreover, it is also possible to apply further
additional functional layers whose adhesion and durability are
substantially improved, for example electrically conductive layers,
readily cleanable or hard layers.
[0020] It is furthermore found that the flame-pyrolytic deposition
can generate a granular surface structure of the layer containing
silicon oxide with silicon oxide grains, or grains containing
silicon oxide, having a diameter of up to at most 80 nanometers,
preferably up to at most 60 nanometers as seen in plan view. The
grains are in this case arranged on the surface of a dense
flame-pyrolytic layer. In the case of such a layer, the term layer
thickness is intended to mean the layer thickness of the dense
layer without the grains arranged thereon.
[0021] The possibility that individual grains with even larger
diameters may also lie on the surface is not precluded. Aggregation
of a plurality of grains may for example take place, which can then
appear as a single grain under the microscope. In any event, more
than 90% of the individual grains perceptible with 200,000 times
magnification in a scanning electron microscope have a diameter of
up to at most 80 nanometers, preferably up to at most 60 nanometers
in layers according to the invention. Larger grains with a larger
diameter, composed of such smaller aggregated grains, may also be
visible. In general, the grains predominantly have diameters of up
to 40 nanometers.
[0022] Such layers containing silicon oxide on a glass ceramic
substrate permit particularly well-adhering coating with further
layers, since a very large surface area can be achieved by the
granular structure of the layer deposited according to the
invention. The susceptibility to scratching is furthermore reduced.
Despite the granular surface, a sufficient barrier effect is
nevertheless induced owing to the dense layer on which the grains
are arranged, in order to avoid haloing which occurs otherwise in
the case of burned-in decoration. Smoothing of the granular surface
structure may then take place after the ceramizing. In this case,
corrugated structures may be formed from the grains.
[0023] According to a refinement of the invention, a subregion of
the layer containing silicon oxide is coated with a hydrophobic
coating. Such a layer may advantageously comprise a sol-gel layer
with a hydrophobic component. A silicate layer, which can be
produced by sol-gel coating, is in particular envisaged in this
case. A fluoroalkylsilane is particularly suitable as the
hydrophobic component.
[0024] In addition to the decorative layer, the substrate may also
be coated with an infrared-reflecting layer. A tin oxide layer is
particularly suitable for this. On such a layer, the
flame-pyrolytic layer containing silicon oxide may also be applied
on the tin oxide layer, in order to act as an adhesion promoter for
the decoration and/or another coating, since the adhesion of a
further layer on a tin oxide layer is often only poor. Conversely,
it has surprisingly been found that a flame-pyrolytic layer
containing silicon oxide according to the invention adheres very
well even on tin oxide. Besides being used as an
infrared-reflecting layer, tin oxide may also be used as a
transparent conducting layer. In particular, fluorine-doped tin
oxide is suitable as such a layer.
[0025] The invention, by which particularly durable decorations can
be applied without bulging, is therefore outstandingly suitable for
example to produce articles for household appliances made of glass
ceramic, such as hobs, oven windows, baking, cooking or frying
vessels, for example a glass ceramic wok.
[0026] The invention is likewise suitable as a barrier layer
against aggressive media resulting from combustible gases and/or
other evaporation components and/or contamination from the heat
treatment environments, which may for example corrode the glass or
the glass ceramic. The invention is therefore also outstandingly
suitable inter alia.gtoreq.irrespective of the way in which
decoration is applied--for glass ceramic reflectors or as a coating
of glass ceramic articles which are exposed to aggressive
combustion products, for example gas-heated glass ceramic hobs or,
inter alia stove, burner or oven windows. The invention thus also
relates to a method for producing a glass ceramic reflector, in
which a glass piece for a reflector is provided and ceramized, and
in a similar way as in the embodiments of the invention described
above, a layer containing silicon oxide is flame-pyrolytically
deposited on the piece by sweeping over at least one region of the
surface of the piece with a flame and hydrolyzing a silicon
compound added to the flame. The layer containing silicon oxide may
also advantageously be used further as a base layer for an applied
decoration, for example a manufacturer logo. Furthermore, the layer
containing silicon oxide may be deposited both before and after the
piece is ceramized. If the layer containing silicon oxide is
deposited after the ceramization, then this layer may also be
applied on further previously deposited layers. In particular, a
one- or multilayer reflective coating of the piece is in this case
particularly envisaged.
[0027] Detrimental long-term effects due to the gas flame exposure
or combustion products in the case of glass ceramic articles such
as glass ceramic hob plates or glass ceramic refractory glasses,
for example stove, burner or oven windows, can likewise be avoided
or at least reduced by flame-pyrolytically depositing a barrier
layer containing silicon oxide on at least one side of the
substrate of the article or the green glass substrate, by sweeping
over with a flame and hydrolyzing a silicon compound added to the
flame. In the context of the invention, the term green glass
substrate refers to the glass substrate before ceramization. In
this case as well, the flame-pyrolytic layer containing silicon
oxide acts as a diffusion barrier which prevents or at least
retards the ingress of combustion residues into the ceramized
layer. In fact, in the case of glass ceramic windows for burners,
ovens or stoves, it is found that these panes are attacked strongly
in the course of time by sulfur oxides being given off. In the case
of such glass ceramic articles as well, the layer containing
silicon oxide may be flame-pyrolytically deposited before or after
the ceramization. These articles may likewise be provided with
decoration, as described above.
[0028] The invention will be explained in more detail below with
the aid of exemplary embodiments and with reference to the
drawings, in which elements which are the same and similar are
provided with the same references and features of various exemplary
embodiments may be combined with one another.
[0029] FIGS. 1A to 1C show method steps for producing a decorated
glass ceramic substrate according to a first embodiment of the
invention,
[0030] FIG. 2 shows a device for carrying out a variant of the
method steps shown with the aid of FIGS. 1A to 1C,
[0031] FIG. 3 shows an embodiment of a substrate producible
according to the invention with an infrared-reflecting and
hydrophobic, or electrically conductive coating,
[0032] FIGS. 4 to 7 shows an exemplary uses of a substrate coated
according to the invention,
[0033] FIGS. 8 and 9 show scanning electron microscopic images of a
flame-pyrolytic layer, and
[0034] FIG. 10 shows a scanning electron microscopic image of a
glass ceramic substrate with a flame-pyrolytic layer after the
ceramization.
[0035] Method steps for producing a decorated glass ceramic
according to a first embodiment of the invention will be explained
with the aid of FIGS. 1A to 1C.
[0036] The method for producing a decorated glass ceramic substrate
is based on producing or providing a glass substrate,
flame-pyrolytically depositing a layer containing silicon oxide on
the glass substrate by sweeping over at least one region of the
surface of the substrate with a flame and hydrolyzing a silicon
compound added to the flame, applying a decorative ink on the layer
containing silicon oxide and then burning in the decoration.
[0037] FIG. 1A shows the step of depositing the layer containing
silicon oxide. A flat substrate in the form of a pane is first
provided. To this end a glass pane of float glass, rolled glass or
glass ceramic produced therefrom, which is produced by separating a
section from a continuously produced floated and/or rolled glass
strip, may in particular be used as the substrate 1.
[0038] In order to deposit the layer 5 containing silicon oxide,
the side 11 of the flat substrate 1 in the shape of a pane in this
example is then swept over with flames 21, by moving the substrate
1 past a burner battery 20 with burners 21 which generate the
flames 22. Instead of or in addition to moving the substrate 1, it
is of course also possible to move the burner battery 20. By
hydrolyzing a silicon compound added to the flame, the layer 5
containing silicon oxide is then deposited on the substrate. In
particular hexamethyldisiloxane (HMDSO), hexamethyldisilazane
(HMDSN), tetraethoxysilane may be added to the flame as the silicon
compound. In the simplest case, to this end the silicon compound in
gaseous form is mixed with the combustible gas. A gas with one or
more of the components hydrogen, methane, propane, butane is
preferably used as the combustible gas.
[0039] The coating parameters relevant for the layer thickness of
the layer 5, inter alia the composition of the combustible gas with
a silicon compound and the speed at which the substrate 1 is moved
past the flames 22, are adjusted so that the layer containing
silicon oxide has a layer thickness of from 1 to 100 nanometers,
particularly preferably 4 to 40 nanometers, and particularly
preferably at most 20 nanometers.
[0040] If a green glass substrate for producing a glass ceramic
article is used as the substrate 1, then the processing step shown
in FIG. 1A produces an intermediate product which has a
flame-pyrolytic layer containing silicon oxide deposited on the
green glass substrate and which, by the flame-pyrolytic layer, is
furthermore provided with certain protection by the layer 5 against
damage during the further treatment. For instance, scratches which
may occur during the further treatment, for example transport on
rollers or placing the substrate on supports and lifting it
therefrom, can be avoided to a certain degree by the smoother
surface and the greater hardness of the layer 5.
[0041] FIG. 1B shows the substrate after the structured application
of ceramic decoration ink 9 onto the layer 5 containing silicon
oxide. In this example, the decorative pattern comprises patterns
in the form of circular hob plate edges 91 and a manufacturer logo
92. The decorative ink 9 with the patterns 91, 92 may for example
be applied by screen printing, electrostatic application, in
particular electrophotographic application, applying a transferable
image, spraying or atomization.
[0042] The ceramic decorative ink is subsequently burned in. This
step is shown by FIG. 1C. In this embodiment of the method
according to the invention, in particular, the decoration is burned
in simultaneously with ceramization of the glass substrate 1, so
that a decorated glass ceramic plate is obtained.
[0043] For ceramizing and simultaneously burning in the decoration,
this end of the substrate with the layer 5 and the decorative ink
applied thereon is put into a ceramizing oven 30. During
ceramization in the oven 30, the glass substrate 1 becomes soft so
that even minor forces acting on the substrate 1 lead to undesired
deformations. During ceramization typically at 900.degree. C. or
above, for instance, 5 viscosities of less than c=10.sup.1 dPas can
be reached. Shrinkage of the substrate furthermore takes place
during the ceramization. The flame-pyrolytically deposited layer 5
does not cause any relevant thermal stresses, in contrast for
instance to thicker sol-gel layers as obtained by the method known
from DE 3936654 C1, so that deformation is avoided. The silicate
layer 5 with the high density of terminal OH groups furthermore
ensures improved adhesion of the decoration after burning in, i.e.
ceramizing. During the ceramization, the green glass substrate is
conventionally placed on a support, typically a ceramic support,
and ceramized. The green glass substrate becomes very soft and
shrinks during the ceramization. The glass may stick to the support
owing to the low viscosity during the ceramization, the glass
becoming detached again during shrinkage so that unsightly surface
damage such as scratches and holes may be created in the surface.
But if before the ceramization, a layer 5 containing silicon oxide
is applied according to the invention on the side lying underneath
during the ceramization, then sticking on the support and
associated damage can be avoided. Furthermore, the layer 5 can also
protect to a certain extent against other damage which may occur as
a result of production, sale and use of the products with such
glass or glass ceramic objects. To this end, for example, unlike as
represented in FIG. 1C, a flame-pyrolytic layer containing silicon
oxide may also be applied on both sides.
[0044] If a layer 5 is applied on one or both sides of the
substrate 1--irrespective of whether or not decoration is applied,
then the substrate 1 may also be used particularly advantageously
as a glass ceramic hob plate for gas cooking or as a glass ceramic
window, for example as a stove, oven or gas burner window. The
layer 5 then acts as a barrier coating against incoming combustion
residues. Inter alia, sulfur dioxide as a typical combustion
product exerts a corrosive effect on the glass ceramic.
[0045] FIG. 2 shows a device 40 for carrying out a variant of the
method steps explained with the aid of FIGS. 1A to 1C. In the
method which can be carried out by the device 40, a continuous
glass strip 10 is first produced. To this end, in melting apparatus
50, a glass melt 52 is generated which emerges from an outlet 53
and is shaped by rollers 54 to form a flat glass strip 10 with
opposite sides 11, 12. As an alternative, the continuous glass
strip 10 may also be produced by floating a glass melt on a tin
bath.
[0046] As explained with the aid of FIG. 1A, the layer 5 containing
silicon oxide is deposited by hydrolyzing a silicon compound in one
or more flames 22 generated by burners 21. In contrast to the
embodiment of the invention as explained with the aid of FIGS. 1A
to 1C, however, in this case the layer 5 is deposited on the side
11 of the continuous glass strip 10 after the rolling.
[0047] The flame 22 has an inner reducing part 23 and an outer
oxidizing part 24. As in the flame-pyrolytic coating shown with the
aid of FIG. 1A, the flame 22 and/or the distance from the substrate
surface to the burner 21 is/are adjusted so that only the oxidizing
part of the flame 22 sweeps over the substrate--i.e. in this case
the glass strip 10.
[0048] In order to produce individualized substrates 1, sections
are subsequently separated by means of a separating device 58. The
separation may for example be carried out by etching a line on the
glass strip 10 and breaking it off. A decorative ink 9 is
subsequently printed on the glass strip 10 by means of a printing
device 56. The printing device 56 may for example be a screen
printing device. The application may likewise be carried out by
electrostatic application, and in particular electrophotographic
application, by applying a transferable image, spraying or
atomization. The individualized substrates 1 with the
flame-pyrolytically deposited layer 5 and the decorative ink 9
printed on are then ceramized in a ceramizing oven 30, the
decoration simultaneously being burned in.
[0049] According to another embodiment of the invention, the
decorative ink is applied before the layer containing silicon oxide
is deposited, so that the layer containing silicon oxide covers
both the decorative ink and the rest of the surface of the
substrate. In order to carry out this embodiment of the method
according to the invention, for example, the arrangement of the
printing device 56 and the burners 21 may be interchanged in the
device represented in FIG. 2.
[0050] FIG. 3 shows an embodiment of a substrate producible
according to the invention with additional functional layers. In
this embodiment of the invention, the substrate is coated on one
side with an infrared-reflecting and/or conductive tin oxide layer
7. A layer 5 according to the invention containing silicon oxide is
subsequently deposited flame-pyrolytically on the sides 11, 12 of
the flat substrate 1, i.e. on both sides. On the side 11, the layer
5 serves as a diffusion barrier to prevent haloing of the
decoration 8 produced on this side by structured deposition of
decorative ink and burning the ink in.
[0051] On the side 12 of the substrate 1, the layer 5 serves as an
adhesion promoter for a subsequently applied hydrophobic layer 13.
Owing to the outwardly pointing terminal OH groups of a layer 5
containing silicon oxide produced by flame pyrolysis according to
the invention, very good adhesion of the layer on the tin oxide
layer 7 is produced, as well as of the hydrophobic layer 13 on the
layer 5.
[0052] The hydrophobic layer 13 is preferably produced by applying
a sol-gel containing silicate, to which a hydrophobic component is
added. Fluoroalkylsilane in particular is suitable as a hydrophobic
coating, so that in this case the layer 13 is a silicate layer
containing fluoroalkylsilane.
[0053] A substrate coated and decorated as shown in FIG. 3 is
suitable, for example as an oven window. If the oven window is
arranged so that the side 12 with the hydrophobic coating 13 and
the infrared-reflecting tin oxide layer 7 delimits the interior of
the oven, then the tin oxide layer 7 reduces the heating of the
window. Owing to the hydrophobic coating, the window is also easy
to clean since the hydrophobic fluoroalkylsilane prevents dirt from
adhering.
[0054] FIG. 4 shows an example of pots and pans or crockery with a
decorated substrate producible according to the invention. The
exemplary embodiment of the invention as represented in FIG. 4
shows a frying vessel, in particular a wok 60 with a lower part 62,
handles 63 fastened on the lower part 62 and a lid 61. According to
the invention, the lower part 62 is flame-pyrolytically provided
with a layer 5 containing silicon oxide. As in the previous
examples, decoration 8 is produced on the layer 5 by applying
decorative ink and burning the decoration in. In this case, it is
again recommendable to burn the decorative ink in by the heat
treatment of the lower part 62 for ceramization.
[0055] Naturally, the lid 61 may also be made of glass ceramic and
comprise decoration applied according to the invention.
[0056] FIGS. 5 and 6 shows two variants of further exemplary
applications of the invention. Both figures represent glass ceramic
reflectors 65, as are used in particular for reflecting the light
of high-performance lamps with a power of more than 200 watts. On
the curved reflector inside 66, which is intended as a reflection
surface for a light source arranged in front of it, the glass
ceramic reflectors 65 respectively comprise reflective coatings 67.
In both variants, this side 66 of the reflector is respectively
also coated with a flame-pyrolytic layer 5 containing silicon.
Similarly as in the exemplary embodiments explained above, the
layer 5 is produced by sweeping over the inside 66 of the piece
with a flame and hydrolyzing a silicon compound added to the
flame.
[0057] In the variant represented in FIG. 5, the reflective coating
67 is applied on the previously deposited flame-pyrolytic layer 5,
while in the example shown in FIG. 6 the layer 5 is deposited on
the reflective coating 67.
[0058] In this example, the layer 5 may also be applied even before
the green glass substrate is ceramized. In both cases, the layer 5
serves as a barrier against the diffusion processes otherwise
occurring under the enormous thermal load on the reflector, which
in the long term can degrade the visual appearance of the
reflector. A layer 5 may also be applied on the outside of the
reflector 65. Decorations, which as described above are produced
according to the invention by using a flame-pyrolytic layer 5 as a
diffusion barrier, may in particular be provided on the inside 66
and/or the outside.
[0059] FIG. 7 shows another example of a product with a glass
ceramic article according to the invention. A stove 70 comprises a
glass ceramic substrate 1 according to the invention as a stove
window 72. The inside of the substrate 1, or of the stove window
72, is coated according to the invention with a flame-pyrolytic
layer 5 containing silicon, as represented by way of example with
the aid of FIG. 1A. The layer containing silicon oxide is used here
as a diffusion barrier or barrier layer, in order to prevent or at
least retard the ingress of combustion products created on the
inside into the stove window 72. Particularly when burning
combustion products containing sulfur--wood, or fossil fuels such
as natural gas or oil--sulfur oxides are formed which can corrode
the glass ceramic of the window 72.
[0060] FIGS. 8 and 9 represent scanning electron microscopic images
of a glass substrate coated with a flame-pyrolytically deposited
layer for subsequent ceramizing. FIG. 8 shows the coated surface in
plan view, and FIG. 9 shows a view of a fracture edge of the coated
substrate. The magnification in the images can be found with the
aid of the scale bars shown under the images. The plan view of the
surface of the flame-pyrolytic layer as shown in FIG. 8 was
recorded with an acceleration voltage of 5 kV at 200,000 times
magnification. The image shown in FIG. 9 was recorded at 300,000
times magnification, likewise with an acceleration voltage of 5
kV.
[0061] Both images show that the surface 55 of the flame-pyrolytic
layer 5 has a granular structure overall, with grains 57 containing
silicon oxide. The grains protrude from the surface of the dense
layer 5, i.e. they are arranged on this surface. More than 90% of
the grains visible on the images have a diameter of less than 80
nanometers, or even less than 60 nanometers. A diameter of up to 40
nanometers is predominantly to be seen in plan view. Owing to this
finely grained surface structure, a particularly large surface area
can be achieved with a visually inconspicuous structure owing to
the small size of the grains. The large surface area in conjunction
with the OH groups present in a high density on the surface of the
layer 5 containing silicon oxide, at least in the freshly deposited
state, ensures particularly good adhesion of subsequently applied
materials such as the decorative ink or further layers. Flattening
of the grains 57 is generally observed after the ceramization, so
that a corrugated surface structure of the layer 5 is obtained.
Often, however, the particles or grains 57 can still be seen after
the ceramization.
[0062] FIG. 10 represents a scanning electron microscopic image of
the edge of a substrate 1 with a layer 5 containing silicon oxide
after the ceramization. The image was recorded with an acceleration
voltage of 10 kV and 350,000 times magnification. The approximately
33 nanometer thicker layer 5 containing silicon oxide can be seen
on the surface of the substrate. The surface 55 is no longer so
conspicuous after the ceramization, although a corrugated structure
is still present and visible after the ceramization and a few
particles are still to be seen in the background.
[0063] It is clear to the person skilled in the art that the
invention is not restricted to the embodiments described above, but
may be modified in a variety of ways. In particular, the features
of the individual exemplary embodiments may also be combined with
one another.
* * * * *